1. Field of the Invention
The present invention relates to an optical system for detecting the shape of a three-dimensional object, and if necessary, a gradation pattern thereof.
2. Description of the Related Art
There are many known non-contact measuring methods of detecting the shape of a three-dimensional object, and these are used, for example, to check the mounting state of electronic components on a printed circuit board. Namely, the presence (or absence) of electronic components, the mounting positions and mounting directions thereof, failures of electronic connection, etc., are automatically detected by a non-contact method using an optical detection system. One of the most widely-used non-contact measuring methods is a structure light method, as discussed below.
FIG. 43 shows the principle of a known structure light method of detecting a shape (particularly the height) of an object.
As shown in the FIG., an object 10 to be detected is illuminated directly from above by a slit light L.sub.1, and lines of light intersecting the object 10 are observed by a TV camera 13 from a predetermined oblique angle. For example, for the shape of the object 10 shown in FIG. 43, the portions corresponding to heights of the object 10 are detected as a luminary image by the TV camera 13, as shown in FIG. 44. An image window of the TV camera is small in comparison with the whole, or complete, object area. By scanning the image window step by step in the lateral direction (x direction) for every line (vertical direction y), the whole shape (height) of the object can be detected by a triangulation method known per se.
In such a known structure light method, however, it takes a long time to scan the image window in the x-y directions, resulting in a reduced measuring speed, and even if a realtime processing of the detection of the height from the detected image picture is attempted by using hardware, it takes at least 1/30 second (time of one frame) to measure the height information in one window. Such a low measuring speed is not satisfactory in view of the current need for an in-line inspection system.